1. Field of the Invention
The present invention relates to an apparatus for and method of generating an phase current instruction value for an alternating current servomotor, and more particularly to a device for generating a phase current instruction value for an alternating current (hereinafter referred to as "AC") servomotor and its method having a driver constructed to drive a synchronous AC servomotor wherein a phase current instruction value for a commutation of the AC servomotor driver can be generated by receiving the detection signal of a commutation sensor which detects the reverse electromotive force of the motor.
2. Description of the Prior Art
A device for generating a phase current instruction value for an AC servomotor thus constructed as above can be found in Japanese laid open patent application No. Hei 2-202392. As depicted in FIG. 1, a velocity loop compensating circuit 1 outputs a torque command Tc by adding or subtracting a velocity variation, namely, the difference between a velocity command Vc and a voltage corresponding to the actual velocity of the servomotor from a frequency/voltage converter 9 connected to the encorder 7.
Multipliers 2U, 2V, 2W are constructed to output the phase current instruction values ir(u), ir(v), ir(w) by multiplying respectively the torque command Tc outputted from the compensating circuit 1 and 120 degree-shifted sine wave signal, and the like, in accordance with the electrical angle of the servomotor rotor outputted from the sine wave signal generating circuits 8U, 8V, 8W on u, v, w phases.
Current loop compensating circuits 3u, 3v, 3w are constructed to add or subtract the current variation. In particular, the difference between the respective phase current command values ir(u), ir(v), ir(w) and the phase current values ic(u), ic(v), ic(w) detected from current detectors 5u, 5v, 5w is determined. The current loop compensating circuits 3u, 3v, 3w are constructed to output phase voltage commands, er(u), er(v), er(w) to power amplifiers 4u, 4v, 4w, respectively.
The power amplifiers 4u, 4v, 4w, comprising transistors, PWM(Pulse Width Modulation) circuits and the like, receive the phase voltage commands er(u), er(v), er(w), and supply the phase voltages er'(u), er'(v), er'(w) to respective phases of the servomotor 6 for driving the servomotor 6.
The device for generating a phase current instruction value for an AC servomotor constructed as described above has problems including complication in construction and an increase in manufacturing costs since the device is implemented in hardware.
Accordingly, it is an object of the present invention to provide a generating device of a phase current instruction value for an AC servomotor and a method thereof, which can generate sine waves for commutation of an AC servomotor driver by receiving as an interrupt a signal from a commutation sensor from a microprocessor.